As a plasma processing device, Patent Document 1 or Patent Document 2 discloses a parallel plate type plasma processing device. The plasma processing device disclosed in Patent Document 1 or Patent Document 2 includes a processing vessel, a gas supply unit, a lower electrode and an upper electrode. In the plasma processing device, a processing gas is supplied into a processing space by the gas supply unit to provide a high-frequency electric field between the lower electrode and the upper electrode. This generates plasma of the processing gas so that a substrate to be processed is processed by, for example, radicals of elements included in the processing gas.